This invention relates to an unsaturated polyester resin composition for treating cathode-ray tubes.
A method for adhering a cathode-ray tube and front glass to each other generally comprises, as shown in the attached drawing, surrounding and holding, in contiguity with a face-plate portion 2 of a cathode-ray tube 1, front glass 3 having the same curvature and substantially the same size as the face-plate portion 2 with a tape 4 at a very short distance from the face-plate portion, filling this gap with a resin composition 5 such as epoxy resin composition, unsaturated polyester resin composition or the like, and then curing the resin composition.
Conventional epoxy resin compositions and unsaturated polyester resin compositions for adhering a cathode-ray tube and front glass to each other have both merits and demerits, and in the existing circumstances, there has not yet been obtained any resin composition having both characteristics and workability which are satisfactory as those of the resin composition for adhering a cathode-ray tube and front glass to each other.
For example, when an epoxy resin composition is used, it has a high adhesive strength and hence is advantageous for adhering front glass to a face-plate portion, but since it has a considerable coloring property, it is not preferable for use in a cathode-ray tube in which color is regarded as important, such as a color cathode-ray tube. Moreover, in the case of a cathode-ray tube having a high added value in itself such as a color cathode-ray tube, its recovery is also regarded as important, and when an epoxy resin is used, it has a high adhesive strength, so that the face-plate portion tends to be injured at the time of removing the front glass, therefore it is substantially impossible to peel off the glass.
Moreover, epoxy resin compositions have a higher viscosity than unsaturated polyester resin compositions and hence are disadvantageous in that foams sucked at the time of mixing with a curing agent or casting the resin are difficult to remove. Furthermore, since epoxy resins increase rapidly in viscosity immediately after being mixed with a curing agent, their period of usability at casting is very short, and for carrying out operations smoothly, special mixing and casting apparatus are needed; thus they are very poor in workability.
On the other hand, when an unsaturated polyester resin composition is used, its viscosity generally is as relatively low as several poises, so that its mixing with a curing agent and its casting into the gap between the face-plate portion of a cathode-ray tube and front glass are easy, and because of its low viscosity, it is advantageous, for example, in that it is easily defoamed at the time of mixing or casting. However, if the proportion of the curing agent of several percent based on the unsaturated polyester resin composition is different from the predetermined condition, distortion is locally caused at the time of curing. This cure distortion results in lens effect, so that when the cathode-ray tube is operated, a striped pattern, luminant spots and the like appear on a screen.
Since these striped pattern and luminant spots impare the value of the product, sufficient care should be taken in the mixing proportion of the curing agent.
The cure distortion is caused also by rapid heating or temperature unevenness of a curing oven, therefore temperature control and the like should be sufficiently carried out.
Unsaturated polyester resin compositions involve many problems in their production as described above, but they are advantageous in that they have a low viscosity and hence is easily defoamed, that they are hardly colored and hence excellent in transparency, and that the cathode-ray tube can be recovered relatively easily. However, they are disadvantageous in that since they are poor in adhesive strength, they peel off from the face-plate portion or the front glass portion when the cathode-ray tube is operated for a long period of time.